Combined damping and lift means for marine propulsion device

ABSTRACT

Disclosed herein is a marine propulsion device including a hydropneumatic or gas spring type shock absorber which is connected between a support bracket and a swivel bracket carrying a propulsion unit to damp angular movement of the propulsion unit during tilting, such as during a sudden upward tilting movement of the propulsion unit caused by striking an underwater obstruction while the boat is traveling at a high forward speed. In one embodiment, the gas pressure of the gas spring unit is at a level whereby the tilting force applied by the gas spring unit to the propulsion unit is slightly less than that required to tilt the propulsion unit from an operating position to a raised elevated position, thereby substantially reducing the effort to manually tilt the propulsion unit to a raised position. In another embodiment, the gas pressure of the gas spring unit is at a level whereby the tilting force applied by the gas spring unit to the propulsion unit is greater than that required to tilt the propulsion unit from an operating position to a raised or elevated position so that, upon releasing the locking means releasably locking the propulsion unit in an operating position, the propulsion unit is automatically tilted to a raised or elevated position by the gas spring unit.

Ilnited 8tates Patent [191 Borst [451 Feb. 4, 1975 [75] Inventor: Gaylord M. Borst, Waukegan, Ill.

[73] Assignee: Outboard Marine Corporation,

Waukegan, Ill.

[22] Filed: Mar. 9, 1973 [21] Appl. No.: 339,587

[56] References Cited UNITED STATES PATENTS 3/1917 Pettengill 267/64 R 4/1940 Greve 267/64 R 2,721,074 10/1955 DeCarbon 267/8 R 2,774,447 12/1956 DeCarbon 188/317 2,823,915 2/1958 DeCarbon 267/8 R 2,992,864 7/1961 DeCarbon 267/64 R 3,003,724 10/1961 Kiekhaefer 248/4 3,158,346 11/1964 Jagger 248/4 3,201,112 8/1965 Wiissner 267/64 R 3,250,501 5/1966 Alexander 248/4 R25,048 10/1961 Hulsebus 115/17 FOREIGN PATENTS OR APPLICATIONS 631,584 1l/l96l Canada 248/4 710,586 6/1965 Canada 248/4 Primary Examiner-Trygve M. Blix Assistant Examiner-Edward R. Kazenske Attorney, Agent, or FirmMichael, Best & Friedrich [57] ABSTRACT Disclosed herein is a marine propulsion device including a hydropneumatic or gas spring type shock absorber which is connected between a support bracket and a swivel bracket carrying a propulsion unit to damp angular movement of the propulsion unit during tilting, such as during a sudden upward tilting movement of the propulsion unit caused by striking an underwater obstruction while the boat is traveling at a high forward speed. In one embodiment, the gas pressure of the gas spring unit is at a level whereby the tilting force applied by the gas spring unit to the propul sion unit is slightly less than that required to tilt the propulsion unit from an operating position to a raised elevated position, thereby substantially reducing the effort to manually tilt the propulsion unit to a raised position. In another embodiment, the gas pressure of the gas spring unit is at a level whereby the tilting force applied by the gas spring unit to the propulsion unit is greater than that required to tilt the propulsion unit from an operating position to a raised or elevated position so that, upon releasing the locking means releasably locking the propulsion unit in an operating position, the propulsion unit is automatically tilted to a raised or elevated position by the gas spring unit.

8 Claims, 2 Drawing Figures COMBINED DAMPING AND LIFT MEANS FOR MARINE PROPULSION DEVICE BACKGROUND OF THE INVENTION This invention relates generally to marine propulsion devices, such as outboard motors. More particularly, this invention relates to devices for damping shock forces imparted to the propulsion unit upon striking an underwater obstruction.

Damping means, such as hydraulic shock absorbers, have been employed in outboard motors to damp the tilting forces imparted to the propulsion unit upon engaging an underwater obstruction while the boat is moving at high forward speeds so that the damage to the motor and/or boat transom is avoided. Some outboard motors, particularly larger ones, are frequently equipped with power means for selectively tilting the propulsion unit to a raised or elevated position for storage or trailering. Kiekhaefer US. Pat: No. 3,003,724, issued Aug. I0, I96] suggests using a hydraulic shock absorber interposed the propulsion unit and the support bracket to serve both as a damping means and a power lift means. However, the system proposed by Kiekhaefer patent requires a separate source of hydraulic pressure connected to the shock absorber and a control assembly, thereby adding to the cost and complexity of the outboard motor.

SUMMARY OF THE INVENTION The invention provides a marine propulsion device including a damping means which is connected between a support bracket and a propulsion assembly including a swivel bracket carrying a propulsion unit,

which damping means is capable of serving the dual function of damping angular movement of the propulsion unit during a sudden tilting movement and of lifting or assisting in lifting the propulsion unit from an operative position to a raised or elevated position.

More specifically, such damping means comprises a fluid pressure damping device including a cylinder which is partially filled with an incompressible liquid, with the remainder of the cylinder being filled with a gas under a predetermined pressure greater than atmospheric, a reciprocative piston inside the cylinder, a piston rod connected to the piston and extending from one end ofthe cylinder, means for pivotally connecting the damping device between the support bracket and the propulsion assembly so that, in response to upward and downward tilting movement of the propulsion unit, the piston rod respectively extends and retracts, and flow control means in the cylinder for controlling the flow of liquid between opposite sides of the piston during reciprocation of the piston to thereby damp the angular movement of the propulsion unit during tilting.

In one embodiment, the gas is pressurized to level whereby the piston-extending force applied to the piston by the liquid and gas, and thus the tilting force applied to the propulsion unit, is slightly less than the tilting force required to tilt the propulsion unit from an operating position to a raised or elevated position. Thus, the damping means effectively and substantially reduces the effort required to manually tilt the propulsion unit from an operating to a raised or elevated position.

In another embodiment, the gas is pressurized to a level whereby the piston-extending force applied to the piston by the liquid and the gas is greater than the tilting force required to tilt the propulsion unit to a raised or elevated position. Thus, the damping means, after release of the locking means which releasably locks the propulsion unit in an operating position, automatically tilts the propulsion unit to a raised or elevated position.

An object of this invention is to provide a marine propulsion device including a simple, inexpensive means which is capable both of damping the shock forces imparted to the propulsion unit upon. impacting an underwater obstruction and of reducing the force required to manually tilt the propulsion unit from an operating position to a raised or elevated position.

Another object of this invention is to provide a marine propulsion device including a simple, inexpensive means which is capable of damping the shock forces imparted to the propulsion unit upon impacting underwater obstruction and of automatically raising the propulsion unit to a raised or elevated position.

Other objects, aspects and advantages of this invention will become apparent upon reviewing the following detailed description, the drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a fragmentary, elevational view of an outboard motor embodying the invention.

FIG. 2 is an enlarged, sectional view of a gas spring unit adapted to serve a dual function in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before explaining the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawing. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purposes of description and should not be regarded as limiting.

Shown in the drawing is an outboard motor 10 which embodies various of the features of the invention. The outboard motor 10 has a propulsion assembly 11 in cluding a propulsion unit 12 and a swivel bracket 14. The propulsion unit I2 includes an engine (not shown) enclosed within a cowl I6, a drive shaft (not shown) which is disposed inside a drive shaft housing 18 and which drivingly connects the engine and a propeller 20 via a propeller shaft 22. The propulsion unit 12 is connected to the swivel bracket 14 for horizontal swinging movement about a generally vertical king pin 24 for steering control of the propulsion unit. The propulsion assembly 11 is fastened to the transom 26 or other supporting member of a boat hull by a support or transom bracket 23. The swivel bracket 14 is connected to the transom bracket 28 for common swinging movement in a vertical plane or tilting of the propulsion unit 12 and the swivel bracket 14 about a transverse horizontal axis provided by a tilt pin 30.

The transom bracket 28 includes a series of apertures 32 adapted to selectively receive a trim adjustment or thrust pin 34 which is normally engaged by the propulsion unit 12 for positioning the propulsion unit at a desird operating position with respect to the vertical.

The outboard motor also includes a suitable reverse lock 38 which, when engaged, prevents upward swinging or tilting of the propulsion unit 12 during normal operation to thereby facilitate operating the propulsion unit in reverse. The reverse lock is arranged in the usual manner with a releasable feature so that, in the event the impact force of the propulsion unit 12 striking an undewater obstruction exceeds a predetermined level while traveling forward, the reverse lock automatically releases to permit upward swinging or tilting of the propulsion unit. The reverse lock also includes a manual release so as to permit manual tilting of the propulsion unit 12 to a raised or elevated position. The reverse lock can be arranged in any suitable manner, so a detailed description and illustration of the same is deemed unnecessary for a complete understanding of the invention. For example, the reverse lock can be arranged in the manner described in Hulsebus US. Pat. No. Re 25,048 issued Oct. 3, 1961, which patent is incorporated herein by reference.

In accordance with the invention, there is connected between the propulsion assembly 11 and the transom bracket 28 a means which is capable of serving the dual function of damping the angular movement of the propulsion unit during tilting and of either assisting in the manual tilting of the propulsion unit to a raised position or automatically tilting the propulsion unit to a raised position upon releasing the reverse lock.

While other arrangements can be employed, in the construction illustrated, such means comprises one or more hydropneumatic shock absorbers or gas spring units 40. The gas spring unit 40 includes a pressure cylinder 42 closed at the lower end by a closure member 44 and a mounting lug 46 projecting from the closure member 44 for pivotally connecting the lower end of the gas spring unit 40 to the transom bracket 28. A piston 50 is slidably disposed within the cylinder 42 and is secured to one end of a piston rod 52 which extends coaxially of the cylinder 42. The piston rod 52 extends slidably through an opening 54 provided in an upper closure member 56 which closes the upper end of the cylinder 42. Suitable packing or sealing means 58 is provided at the opening 54 and surrounds the piston rod 52 to insure a fluid tight seal between the piston rod 52 and the upper closure member 56.

Attached to the outer end of the piston rod 52 for pivotally connecting the upper end of the gas spring unit 40 to the swivel bracket 14 is a mounting lug 62. The gas spring unit 40 is connected between the swivel bracket 14 and the transom bracket 28 so that the movement arm between the center of the mounting lug 62 and pivot axis of the tilt pin remains substantially constant as the propulsion unit 12 is moved through a tilt arc.

Partially filling the cylinder 42 is a predetermined quantity of a substantially incompressible liquid 64, such as oil or a hydraulic fluid. The liquid 64 is pressurized by a suitable inert gas 66, such as nitrogen or air, which is initially confined in the space above the upper surface of the liquid 64 and is under a predetermined pressure above atmospheric. Thegas 66 usually becomes at least partially dispersed within the liquid after one or more reciprocative cycles of the piston 50.

In order to allow the piston 50 to reciprocate axially within the cylinder 42, means are provided in the cylinder 42 to permit a controlled flow of the liquid 64 from one side to the other side of the piston 50. While various arrangements can be used, in the construction illustrated, such flow control means comprises at least one orifice 68 extending axially through the piston 50.

The piston rod 52 of the gas spring unit 40 extends and retracts with respective upward and downward swinging or tilting movement of the propulsion unit 12 about the tilt pin 30 to damp the angular movement of the propulsion unit and thereby substantially reduce the severity of the impacts at the top and bottom of the propulsion unit swing. The speed of travel of the piston 50 and, thus the amount of damping provided by the gas spring unit 40, depends upon the flow rate of the liquid through the flow control orifice 68.

In order to accommodate abnormally high shock loads on the propulsion unit 12, means can be provided in the cylinder 42 to selectivly permit a by-pass flow of the liquid 64 from one side to the other side of the piston 50 so that the propulsion unit can tilt rapidly and clear the underwater obstruction. While various arrangements can be used, in the construction illustrated, such means comprises at least one relief valve 70 including a by-pass valve orifice 72 which extends axially through the piston 50 and which has a flow area substantially greater than the flow control orifice 68, a shoulder 74 within the by-pass orifice 72 forming a seat for a ball valve 76, and a relief spring 78 urging the ball valve 74 against the shoulder 74. The relief valve 70 opens to permit the liquid to flow from the top side to the bottom side of the piston 50 when the differential pressure across the piston 50 exceeds a predetermined level corresponding to an abnormally high shock load imparted to the propulsion unit 12 causing the piston rod 52 to extend.

Since the flow control orifice 68 extends through the piston 52, equal fluid pressure acts on both sides of the piston during normal operation. The piston rod 52 reduces the effective area on which the pressure can exert a force on the top side of the piston 50, so there is a net pressure force tending to extend the piston rod 52. This net pressure force decreases in accordance with recognized gas laws as the piston rod 52 extends because of an increase in the available volume within the cylinder 42 corresponding to the volume occupied by the portion of the piston rod 52 removed from the cylinder.

In accordance with one embodiment of the invention, the areas of the piston 50 and the piston rod 52, the volume of the liquid 64, and the pressure and volume of the gas 66 are balanced so that the net pressure force acting on the piston 50 to extend the piston rod 52 is closely matched to, but is less than, the force required to counterbalance the weight of the propulsion assembly 11 as it is tilted upwardly about the tilt pin 30.

As the propulsion unit 12 is tilted upwardly from an operating position to a raised, non-operating position, the force required to counterbalance the weight of the propulsion assembly 11 gradually decreases because of a reduction of the horizontal distance between the transverse horizontal pivot axis provided by the tilt pin 30 and the center of gravity of the propulsion unit. This, with the net pressure acting on the gas spring piston 50 decreasing as the piston rod 52 extends, the tilt assist force provided by the gas spring unit 40 remains below that required to counterbalance the weight of the propulsion assembly 11 during the entire tilt arc. Preferably, the above-mentioned variables are balanced so that the difference between the tilt assist force provided by the gas spring unit 40 and the force required to counterbalance the propulsion assembly 11 remains relatively constant throughout the entire tilt are.

For example, in order to tilt a conventional propulsion assembly from a vertical operating position through a 70 arc to a non-operating position, the force required at the location of the gas spring unit attachment to the swivel bracket decreases substantially from about 700 lbs. to about 300 lbs. A gas spring unit having a piston rod with a cross-sectional area of 0.44 square inches and a 4 inch maximum stroke and 0.88 cubic inches ofair (initial volume before pressurization and with the piston bottomed) at a pressure of 1,360 psi. will provide a tilt assisting force at the location of the swivel bracket attachment which decreases substantially linearly from about 600 lbs. to about 240 lbs. through the same tilt arc. By using such a gas spring unit in accordance with the invention, it can be seen that the amount of force required to tilt the propulsion unit is reduced by more than 50 percent. If desired the tilt assisting force provided by the gas spring unit can be more closely matched with the force required to tilt the propulsion unit.

In operation, when the propulsion unit strikes an underwater obstruction while the boat is traveling at a high forward speed, the propulsion unit 12, after the reverse lock has released, tilts upwardly (i.e., tilts counterclockwise as viewed in H6. 1). This movement of the propulsion unit 12 extends the piston rod 52 causing the piston 50 to be displaced upwardly. The piston 50 initially travels at a relatively high speed until the gas 66 is compressed and then moves more slowly through the liquid 64, as the liquid is forced through flow control orifice 68, to damp the angular movement of the tilting propulsionunit 12. Thus, the propulsion unit 12 is permitted to initially tilt upwardly at a high rate upon striking an underwater obstruction so as to quickly clear the obstruction and thereby minimize damage and, yet the angular movement of the propul sion unit is damped to minimize the shock load at the top of the swing and thereby prevent damage to the outboard motor and/or the boat transom.

After clearing the obstruction, the propulsion unit 12 is returned to an operating position by gravity. This re turn movement of the propulsion unit 12 retracts the piston rod 52 causing the piston 50 to be displaced downwardly and slowly through the liquid 64 as the liquid is forced through the flow control orifice 68. The forwarq thrust provided by the propeller 20, when in the water, aids in returning the propulsion unit 12 into locking engagement with the reverse lock 38.

In accordance with another embodiment of the invention, the areas of the piston 50 and the piston rod 52, the volume of the liquid 64, and the pressure and volume of the gas 66 are balanced so that the net pressure force acting on the piston 50 to extend the piston rod 52 (i.e., the tilting force provided by the gas spring unit 40) is greater than the force required to counterbalance the weight of the propulsion unit 12 about the tilt pin 30, but less than that required to release the reverse lock. Thus, with this embodiment, the gas spring unit 40, after the reverse lock is manually or Otherwise released, automatically tilts the propulsion unit 12 to a raised, non-operating position. Because of the controlled flow of the liquid 64 through the piston flow control orifice 68 as the piston rod 52 extends, the angular movement of the propulsion unit 12 is clamped as described above. With this embodiment, the propulsion unit 12 is returned to an operating position by manually pushing downwardly on the propulsion unit to overcome the tilting force provided by the gas spring unit 40 or by a separate lift means adapted to tilt the propulsion unit downwardly. in order to minimize the return force required, the tilting force provided by the gas spring unit 40 is preferably adjusted to a level relatively close to the force required to counterbalance the weight of the propulsion unit, particularly when a manual return is used.

Various features of the invention are set forth in the following claims.

I claim:

1. A marine propulsion device comprising a support bracket adapted to be attached to a boat hull, a propulsion assembly including a swivel bracket and a propulsion unit carried by said swivel bracket, means connecting said propulsion assembly and said support bracket on a horizontal transverse axis for tilting movement of said propulsion assembly in a vertical plane between an operating position and a raised, nonoperating position, and cylinder-piston means for facilitating manual tilting movement of said propulsion assembly upwardly about said axis when said support bracket is attached to a boat hull and for absorbing shock in the event said propulsion assembly strikes an underwater obstacle, said cylinder-piston means comprising a cylinder including a first end and a second end, means for pivotally connecting said first end of said cylinder to one of said support bracket and said propulsion assembly, a piston located in said cylinder for reciprocative movement therein between a position adjacent said first cylinder end when said propulsion assembly is in the operating position and a position adjacent said second cylinder end when said propulsion assembly is in said raised position, means affording restricted fluid flow from one side of said piston to the other in both directions to control the rate of tilting movement between said support bracket and said propulsionassembly, a piston rod connected to said piston and extending from said second end of said cylinder, means for pivotally connecting said piston rod to the other of said support bracket and said propulsion assembly whereby, in response to an upward tilg movement of said propulsion assembly, said piston rod extends and, in response to a downward tilting movement of said propulsion assembly, said piston rod retracts, a predetermined quantity of an incompressible liquid partially filling said cylinder, and a pressurized gas at a pressure higher than atmospheric pressure filling the remainder of the otherwise unoccupied space inside said cylinder.

2. A marine propulsion device according to claim 1 wherein said fluid flow means comprises an aperture extending axially through said piston.

3. A marine propulsion device according to claim 1 wherein the pressure of said gas is at a level whereby the force applied on said piston by said liquid and said gas and acting to extend said piston rod is less than the I tilting force required to tilt said propulsion unit from said operating position to said raised non-operating position, thereby reducing the force required to tilt said propulsion unit from said operating position to said raised position.

4. A marine propulsion device according to claim 1 including locking means acting between said swivel bracket and said support bracket for releasably locking said propulsion unit in said operating position, and wherein the pressure of said gas is at a level whereby the force applied on said piston by said liquid and said gas and acting on said piston to extend said piston rod is greater than the tilting force required to tilt said propulsion unit from said operating position to said raised non-operating position, whereby, when said locking means is released, said piston rod extends to thereby tilt said propulsion unit towards said raised non-operating position.

5. A marine propulsion device according to claim 1 wherein said piston includes one side in opposing relation to said first end of said cylinder and a second side in opposing relation to said second end of said cylinder and further including by-pass flow means in said cylinder for selectively permitting fluid flow from said second side to said first side of said piston in response to extension of said cylinder piston assembly when the differential pressure across said piston exceeds predetermined level in response to a sudden upward tilting movement of said propulsion unit and for preventing fluid flow from said first side to said second side of said piston in response to contraction of said cylinder piston assembly.

6. A marine propulsion device according to claim 5 wherein said by-pass flow means comprises a pressure relief valve means in said piston.

7. A marine propulsion device in accordance with claim 1 wherein said piston has a first side in facing relation to said first cylinder end and a second side in facing relation to said second cylinder end and said cylinder-piston assembly further includes passage means in said piston having means for affording fluid flow through said passage means from said second side to said first side of said piston and preventing fluid flow through said passage means from said first side to said second side of said piston.

8. A marine propulsion device comprising a support bracket adapted to be attached to a boat hull, a propulsion assembly including a swivel bracket and a propulsion unit carried by said swivel bracket, a tilt pin connecting said propulsion assembly and said support bracket on a horizontal transverse axis for tilting movement of said propulsion assembly in a vertical plane between an operating position and a raised. nonoperating position, cylinder-piston means for facilitating manual tilting movement of said propulsion assembly upwardly about said axis when said support bracket is attached to a boat hull and for absorbing shock in the event said propulsion assembly strikes an underwater obstacle, said cylinder-piston means comprising a cylinder-piston assembly pivotally connected between said support bracket and said propulsion assembly, said cylinder-piston assembly being substantially fully contracted when said propulsion assembly is in the operating position and being substantially fully extended when said propulsion assembly is in the raised position, and extending generally vertically throughout movement of said propulsion assembly between the operating and raised positions, a predetermined quantity of an incompressible liquid partially filling said cylinderpiston assembly, and a pressurized gas at a predetermined pressure higher than atmospheric pressure filling the remainder of the otherwise unoccupied space inside said cylinder-piston assembly. 

1. A marine propulsion device comprising a support bracket adapted to be attached to a boat hull, a propulsion assembly including a swivel bracket and a propulsion unit carried by said swivel bracket, means connecting said propulsion assembly and said support bracket on a horizontal transverse axis for tilting movement of said propulsion assembly in a vertical plane between an operating position and a raised, non-operating position, and cylinder-piston means for facilitating manual tilting movement of said propulsion assembly upwardly about said axis when said support bracket is attached to a boat hull and for absorbing shock in the event said propulsion assembly strikes an underwater obstacle, said cylinder-piston means comprising a cylinder including a first end and a second end, means for pivotally connecting said first end of said cylinder to one of said support bracket and said propulsion assembly, a piston located in said cylinder for reciprocative movement therein between a position adjacent said first cylinder end when said propulsion assembly is in the operating position and a position adjacent said second cylinder end when said propulsion assembly is in said raised position, means affording restricted fluid flow from one side of said piston to the other in both directions to control the rate of tilting movement between said support bracket and said propulsion assembly, a piston rod connected to said piston and extending from said second end of said cylinder, means for pivotally connecting said piston rod to the other of said support bracket and said propulsion assembly whereby, in response to an upward tilg movement of said propulsion assembly, said piston rod extends and, in response to a downward tilting movement of said propulsion assembly, said piston rod retracts, a predetermined quantity of an incompressible liquid partially filling said cylinder, and a pressurized gas at a pressure higher than atmospheric pressure filling the remainder of the otherwise unoccupied space inside said cylinder.
 2. A marine propulsion device according to claim 1 wherein said fluid flow means comprises an aperture extending axially through said piston.
 3. A marine propulsion device according to claim 1 wherein the pressure of said gas is at a level whereby the force applied on said piston by said liquid and said gas and acting to extend said piston rod is less than the tilting force required to tilt said propulsion unit from said operating position to said raised non-operating position, thereby reducing the force required to tilt said propulsion unit from said operating position to said raised position.
 4. A marine propulsion device according to claim 1 including locking means acting between said swivel bracket and said support bracket for releasably locking said propulsion unit in said operating position, and wherein the pressure of said gas is at a level whereby the force applied on said piston by said liquid and said gas and acting on said piston to extend said piston rod is greater than the tilting force required to tilt said propulsion unit from said operating position to said raised non-operating position, whereby, when said locking means is released, said piston rod extends to thereby tilt said propulsion unit towards said raised non-operating position.
 5. A marine propulsion device according to claim 1 wherein said piston includes one side in opposing relation to said first end of said cylinder and a second side in opposing relation to said second end of said cylinder and further including by-pass flow means in said cylinder for selectively permitting fluid flow from said second side to said first side of said piston in response to extension of said cylinder piston assembly when the differential pressure across said piston exceeds predetermined level in response to a sudden upward tilting movement of said propulsion unit and for preventing fluid flow from said firsT side to said second side of said piston in response to contraction of said cylinder piston assembly.
 6. A marine propulsion device according to claim 5 wherein said by-pass flow means comprises a pressure relief valve means in said piston.
 7. A marine propulsion device in accordance with claim 1 wherein said piston has a first side in facing relation to said first cylinder end and a second side in facing relation to said second cylinder end and said cylinder-piston assembly further includes passage means in said piston having means for affording fluid flow through said passage means from said second side to said first side of said piston and preventing fluid flow through said passage means from said first side to said second side of said piston.
 8. A marine propulsion device comprising a support bracket adapted to be attached to a boat hull, a propulsion assembly including a swivel bracket and a propulsion unit carried by said swivel bracket, a tilt pin connecting said propulsion assembly and said support bracket on a horizontal transverse axis for tilting movement of said propulsion assembly in a vertical plane between an operating position and a raised, non-operating position, cylinder-piston means for facilitating manual tilting movement of said propulsion assembly upwardly about said axis when said support bracket is attached to a boat hull and for absorbing shock in the event said propulsion assembly strikes an underwater obstacle, said cylinder-piston means comprising a cylinder-piston assembly pivotally connected between said support bracket and said propulsion assembly, said cylinder-piston assembly being substantially fully contracted when said propulsion assembly is in the operating position and being substantially fully extended when said propulsion assembly is in the raised position, and extending generally vertically throughout movement of said propulsion assembly between the operating and raised positions, a predetermined quantity of an incompressible liquid partially filling said cylinder-piston assembly, and a pressurized gas at a predetermined pressure higher than atmospheric pressure filling the remainder of the otherwise unoccupied space inside said cylinder-piston assembly. 